CHAPTER I. 
THE CONSTITUTION OF MILK. 
1. Uses of Milk. 
Cows’ milk is given for the primary purpose of nourishing 
the young calf until it can seek its own food. Man has diverted 
milk from its original purpose and has made it one of the most 
important human foods. The cow originally gave only enough 
milk to nourish its calf until this could take care of itself and, 
therefore, produced milk for only a brief period of time; but 
the modern dairy cow has been gradually developed by intelli- 
gent selection, feeding, and breeding so that she produces milk 
in large quantities and for nearly an entire year after each 
calving. Aside from its use for direct consumption, milk is 
used for the manufacture of a number of human food products, 
like cream, butter, cheese, condensed milk, ete. 
2. Composition of Milk. 
Since milk was by nature intended for the nourishment of 
the calf, one might expect to find that it contains all the food 
elements necessary for the building up of the young animal’s 
body. An analysis reveals the presence of water, which is ab- 
solutely necessary for the maintenance of life; ash is needed for 
the bones; nitrogenous material in the form of casein and albu- 
men, ete., nourishes the muscles, hair, hoofs and horns; and car- 
bonaceous matter in the form of sugar and fat maintains the 
heat of the body. We shall now consider briefly the main char- 
acteristics of the various components of milk. 
3. Albuminoids or Proteids. 
The albuminoids or proteids contain the nitrogen of the milk 
and consist mainly of two substances, casein and albumen. 
Casein. The casein is the part of the milk that is curdled by 
rennet or weak acids. It is commonly supposed to be dissolved 
m the water of the milk, but this is not strictly true. If milk 
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